one can represent the \(\beta (s,u,Q^2)\) 
in terms of two dilogarithms [1]}:
\(\beta (s,u,Q^2) = - {\rm Li}_2\biggl (1-\frac{Q^2}{s}\biggr )- {\rm Li}_2\biggl (1-\frac{Q^2}{u}\biggr )- \frac{1}{2} \, \log ^2\frac{s}{u} - \frac{\pi ^2}{6} \,.\) 
